74 lines
3.8 KiB
JavaScript
74 lines
3.8 KiB
JavaScript
/**
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* localize-labels.js — show the BASEMAP's place names in the reader's language, on both engines.
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*
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* WHY. Every map translated its own chrome but left the basemap's country, city and street names in
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* the style's default (English for Mapbox, Latin + native script for OpenFreeMap), in all eleven
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* locales. A reader in Arabic saw an Arabic legend over an English map.
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*
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* TWO ENGINES, TWO MECHANISMS — each the engine's own supported one:
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* Mapbox map.setLanguage(lang). The engine localizes its own styles, including the Standard
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* style's IMPORTED basemap, which a layer-by-layer rewrite cannot reach.
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* MapLibre OpenFreeMap styles label from OSM name tags, so each basemap symbol layer's text-field
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* is pointed at ['coalesce', name:<lang>, name:latin, name]: the translated name where
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* OSM has one, else the style's Latin name, else the local name. English restores each
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* layer's ORIGINAL expression (remembered per map), so switching back loses nothing.
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*
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* ★ ONLY THE BASEMAP'S LABELS. Plugins add their own symbol layers (zone titles, people-group names,
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* counts) that read their OWN properties. A layer is rewritten only when its text-field reads an OSM
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* name field (name, name:latin, name:nonlatin, name_en, name_int, name:en). Anything else is not a
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* basemap label and is never touched.
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*
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* Fail-soft everywhere: a label that stays in the default language is a nicety lost, never a broken
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* map.
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*/
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const OSM_NAME_FIELD = /\[\s*"get"\s*,\s*"name(?::latin|:nonlatin|:en|_en|_int)?"\s*\]|\{name(?::latin|:nonlatin|:en|_en|_int)?\}/
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const originals = new WeakMap() // map -> Map(layerId -> original text-field)
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function isMaplibreMap(map) {
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return typeof window !== 'undefined' && !!window.maplibregl && map instanceof window.maplibregl.Map
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}
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/**
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* Point the basemap's place-name labels at `lang` (every language, English included).
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* Call after style.load, and again whenever the reader's language changes.
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* @returns {number} how many label layers were localized (0 on Mapbox, which localizes internally)
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*/
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export function localizeBasemapLabels(map, lang) {
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if (!map || !lang) return 0
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const code = String(lang).split('-')[0].toLowerCase()
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try {
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if (!isMaplibreMap(map)) {
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if (typeof map.setLanguage === 'function') map.setLanguage(code)
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return 0
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}
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const style = map.getStyle && map.getStyle()
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if (!style || !Array.isArray(style.layers)) return 0
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let saved = originals.get(map)
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if (!saved) { saved = new Map(); originals.set(map, saved) }
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let n = 0
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for (const layer of style.layers) {
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if (layer.type !== 'symbol' || !layer.layout || layer.layout['text-field'] == null) continue
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const current = layer.layout['text-field']
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const json = JSON.stringify(current)
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// Our own expression is recognisable by shape. Anything ELSE is the style's current original —
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// re-saved every time, so a setStyle() that reuses layer ids with new expressions (a theme
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// switch) never restores the PREVIOUS style's labels.
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if (!json.startsWith('["coalesce",["get","name:')) {
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if (!OSM_NAME_FIELD.test(json)) continue // a plugin's own label: leave it
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saved.set(layer.id, current)
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} else if (!saved.has(layer.id)) continue
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// English too, not the style's own bilingual labels ("Россия" under "Russia"): those drew every
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// native script at world view, so an English page fetched 13 extra glyph ranges (~600 KB, rega:
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// Prayer Progress 18 requests / 777 KB in en against 5 / 185 KB in ar). One language per label.
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const next = ['coalesce', ['get', 'name:' + code], ['get', 'name:latin'], ['get', 'name']]
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map.setLayoutProperty(layer.id, 'text-field', next)
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n++
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}
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return n
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} catch (_) {
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return 0
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}
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}
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export default localizeBasemapLabels
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